A torchlight flashes down the dimly lit alley that has become a favourite drug-dealing hotspot for a local gang. “You’ll hear them before you see them – you’ll hear them scattering,” whispers Chris Smith, a delivery driver turned amateur crimefighter.

Around another dark corner, a suspicious-looking car speeds away when Smith and his group approach. It moves too quick for them to take its registration plate. But the car will be back – and so will the vigilantes.

Smith and his colleagues at Shirley Street Watch have become the scourge of low-level criminals in their little corner of Solihull in the West Midlands since they started patrols in January. Police credit them with effectively forcing drug dealers away from parts of the suburb and significantly reducing antisocial behaviour.

While Smith bristles at the term “vigilante”, the volunteers are one of a rising number of groups springing up across Britain as crime surges and police officer numbers hit a record low. Added into the mix is the very low and falling detection rate – 75% of thefts unsolved. Victims of crime are willing to take matters into their own hands.

This week Hartlepool was called the town “where the police don’t come out” in reports about a neighbourhood group formed to try to fill the void left by police. On one recent Saturday not a single officer was on duty in the town of 92,000 as all were called to another job.

A new Midlands-based group, We Stand Determined, has amassed nearly 3,000 members on Facebook in the past week, with splinter groups already forming in Manchester and elsewhere. Wayne Dean, a former college teacher, said he founded the group after becoming exasperated at the police response to a spate of carjackings in his area of Chelmsley Wood, a housing estate in Solihull.

Dean, 47, described the group as “vigilantes with a twist” and said they had patrolled the streets in the early hours of the morning to try to deter criminals. “We need more police on the street – it’s getting ridiculous now. It’s getting worse and worse by the day,” he said. “People aren’t scared because they know the police aren’t going to turn up. If Theresa May doesn’t do something soon, I wouldn’t like to think what it’s going to be like.”

Chris Smith speaks to young people while on the night patrol around Shirley. Photograph: Fabio de Paola for the Guardian

The emergence of these unofficial groups, formed on social media, has led to fears among the police that a new breed of “have-a-go heroes” are putting themselves at risk and jeopardising investigations. Insp Iftekhar Ahmed, of West Midlands police, told the Guardian he was concerned that well-meaning citizens were “hindering the situation” by taking matters into their own hands.

Ahmed runs the force’s Street Watch scheme of 350 volunteers who patrol neighbourhoods under the supervision of the police, who pay for their insurance and provide a basic training course on safety. The West Midlands project is thought to be the largest in the country – and officers hope to boost it to more than 1,000 volunteers by next year.

Ahmed denied it was “policing on the cheap” for a force that has lost 2,300 officers and had £175m cut from its budget since 2010. He said: “Citizenship is what they’re doing: look, see, report, don’t have a go – that’s the ethos. They’re a vigilant group, not a vigilante group.”

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Smith, a burly former prison guard, leads a team of 12 on patrols most nights of the week in Shirley. The volunteers include a midwife, a plumber, a teacher, a friendly rottweiler called Spirit and a 15-month-old French bulldog called Monty. The group have clocked up 804 hours on patrol since January.

David Jamieson, the West Midlands police and crime commissioner, awarded the group a £4,950 grant this year and credited them with pushing drug-dealing away from a notorious stretch of Stratford Road, a major thoroughfare leading to Birmingham.

Smith said residents were “majorly disappointed” when Shirley police station shut down two years ago – one of 27 West Midlands police buildings closed as a cost-cutting measure. There are concerns about the potential impact on the town of 123,000 when its main police station closes in 2020.

“The government are never going to turn around and say: ‘Bugger, we got it wrong, let’s put a load of bobbies back on the beat.’ It’s never gonna happen,” said Smith.

“We have had a couple of people say: ‘You’re just policing on the cheap.’ But things aren’t going to change any time soon. If you want to make a difference you’ve got to get boots on the ground, you’ve got to get off your arse and do something for your community.”